DE2749855C2 - Voltage regulator circuit - Google Patents

Description

The invention relates to a voltage regulator circuit according to the preamble of claim 1 (U.S. Patent 3,617,859).

; Voltage regulators of monolithic bandgap design with active feedback are known. They replaced

the low power discrete, modular and hybrid voltage regulators that use Zener diode sources. The relatively wide interconnection of the band gap regulator circuit gen can be traced back to the fact that they allow better Leltungs- and load control at low cost.

Bandlücl'n voltage regulator circuits generally contain an internal voltage reference source, a separate error amplifier and a power output stage. The one generated by the reference voltage source The value of the reference voltage is an appropriately chosen fraction of the desired output voltage. The error amplifier then compares the reference voltage with a fraction of the actual output voltage and causes the output stage to keep Ue equal to both voltages compared. Through this feedback an actual output voltage is generated, which is continuously kept at the desired level.

Voltage regulator circuits of the bandgap type have received this designation, because the reference voltage sources generate a zero temperature coefficient reference voltage which is proportional to the bandgap voltage of the semiconductor material by dividing the difference ΔV _K between the base Em ^ r voltage of two associated transistors is generated, this Δ K _{S £} voltage value is reduced in a suitable manner and this reduced Δ K _{B £} voltage value is added to the Basls-Emltter voltage of another transistor. The reference voltage generated in this way is usually an integer multiple of the band gap voltage of the semiconductor. A bandgap control device of this type, in which variable collector currents are used in a monolithic integrated circuit, is described in U.S. Patent '36 17 859. One A description of this type of control device with variable emitter areas can also be found in the Article by A. P. Brokaw, "A Simple Three-Termlnal IC Band Gap Reference" In "IEEE Journal of Solid State Circuits ", Volume SC-9 No. 6, Dec. 1974, p. 388.

When Voltage Regulator Circuits · Of The Band Gap Type Which In Monolithic Integrated Circuits that form the reference voltage source, the error amplifier and the associated control

so circuit the active area of the circuit in the order of magnitude of up to half or more. the Unit costs can be reduced considerably if the space required for each controller circuit on the Half-Parent Tile is lowered as more regulator circuits are then made per Half-Parent Tile and less material is required per function. Alternatively, the reduction of the required Area of the half-liner plate open up the possibility of additional circuits and, accordingly, additional To accommodate borrowed functions on the same chip area as was previously the case.

A voltage regulator circuit with an internal zero temperature coefficient reference voltage source is known from the aforementioned US Pat. No. 3,617,859, which generates a reference voltage which is proportional to a semiconductor material bandgap voltage. This circuit also has an output amplifier connected voltage regulator network; an input of the error amplifier is connected to a branch of the voltage plate network and another input is coupled to the reference voltage source, while the output of the error amplifier is coupled to the input of the output amplifier.

This voltage regulator circuit has the disadvantage already described that the reference voltage source, the error amplifier and the associated control _{circuit occupy the order of magnitude of V 3} to V _{3 of} the active area of the circuit, and this proportion can increase to 80% in circuits with lower power. Of the The invention is therefore based on the object, in a voltage regulator circuit of the type indicated at the outset to reduce the number of components while maintaining the corresponding functions or in one Circuit to allow a larger number of operations to be performed.

This object is achieved in a voltage regulator circuit according to the preamble of claim 1 by the

49 855

Characteristics of the identification number solved.

With regard to the state of the art, reference is also made in this context to “IEEE Transactions Broadcast & Television Receivers ", Volume BTR-18, 2nd time 1972, pp. 73-76. In this publication by staff The Fairchild Camera and Instrument Corporation will be informed of recent developments in the field of monolithic voltage regulator circuits reported. 4 and 5 and the associated parts of the description on the rare 74 and 75 of the cited reference describe voltage control circuits with an internal Zero temperature coefficient reference voltage source which generates a reference voltage »which is proportional a semiconductor material bank gap voltage and in which error amplifiers are integrated.

The invention is described in more detail below with reference to the drawings. ; ■ ■ .......

1 shows a general block diagram of a bandgap voltage regulator of known type. Ό

Fig. 2 is a block diagram of the voltage regulator circuit according to the invention, soft in combination a reference voltage source and error amplifier.

FIg. 3 contains a schematic representation; the circuit according to the invention to explain the Function as a reference voltage source. ,.

Flg.4 is a schematic representation of the circuit according to the invention to show how it works as an error amplifier. : _{; ::} ·. . ; _: . _; ; .-. ■ ..- .. ^. ■ · ...-: - ..:> · -. -; -. · - ·.? "'; ■

The operation of a Bandlür.ken voltage regulator circuit is described in general with the aid of FIg- Λ. The function In detail, data sheets for belt gap control devices can be found, for example the Fairchild UA7800 series. In the. in, Fig. 1, the voltage of the input line is applied to terminal 17. A current source 9 applies a voltage current to error amplifier 11 and to current amplifier 12, and this causes output transistor 13 to supply current to the output terminal 16 and to that consisting of resistors Γ4 and 15. Output control network to be allowed through. First! The voltage applied to the plate network is rarely limited by the. Combined current amplifications of the current amplifier 12 and the output transistor 13 *, however, the reference voltage source 10 in combination with the feedback process ultimately determines the output voltage applied to terminal 16 in the manner described below. The output of the reference voltage source 10 is introduced as an input to the error amplifier Ii, which is usually a two-stage operational amplifier. The other input to the error amplifier U is taken from terminal 19 in the middle switching point of the output voltage divider network, which is formed by resistors 14 and 15. The output current of the error amplifier 11 is fed into the current amplifier 12, the output of which controls the power output transistor 13, which controls the voltage present at terminal 16. The voltage at node 19 must be equal to V _R ; otherwise an error signal is generated by error amplifier 11 and this causes current amplifier 12 to generate a new voltage at the base of power output transistor 13, thereby keeping the voltage present at terminal 16 at a constant value. The values of the resistors 14 and 15 are chosen so that the voltage V _R is applied to the node 19 when the output or load voltage at terminal 16 has the desired value of the output voltage. The output voltage at terminal 16, based on the values of the resistors, is

From -

... Vr (Ru + R \ s)

This active feedback control system allows very good line and load control, however it requires separately a reference voltage source 10 and an error amplifier 11. In Fig. 2 is a bandgap voltage regulator shown according to the invention in the block diagram. It can be seen from this illustration that this circuit fulfills the same general function, with reference voltage source / error amplifier 20 are combined. As described above, the value of the output voltage at terminal 25 can be represented by the following formula:

_v _ K Rv, + fr .;) Vr

In the representation of Flg. 2 Is the combination 20 of reference voltage source and error amplifier generally shown as an operational amplifier, which has a consciously relatively high compensation voltage with specified values of polarity, temperature coefficient and magnitude. Further details can be found, for example, in Tobey et al. "Operational Amplifiers: Design and Applications". As will be explained in more detail below, the combined circuit works simultaneously in different working environments, so that the two desired functions can be made available. Such a simultaneous operation is possible because the Bezugsspannungsquellle in Glelchslrombelrleb work ^1, namely when the voltage values of the order of volts, while the! • ■ ehlcrvcrsiürkerfunktlon Ir ¹ I AC operation works, namely ω with nled.igen voltages in the order of magnitude of millivolts. Every function of the error amplification takes place by modulating the function of the iic / .ugss voltage source.

Hlnc circuit which combines the functions of error amplification and reference voltage source is found within dashed lines 45 in Flg. 3 shown; it is drawn out separately in Flg. 4. The circuit is in Flg. 3 shown with additional components to describe the operating environment, In which it fulfills the function of a pull-out voltage source. From Flg. 4 In particular, it can be seen that the schallung In the operation of the reference voltage source Is identical to the circuit in the Arbeltswelse of the Fchlcrvcrstilrkcrs. The difference between the two types of work is as described in more detail below

will be, In the nature of the entrances and exits and In the points in which the entrances are introduced and the outputs are taken from the circuit.

In the following description it is assumed that npn translators with a high Beu-Wcrt (transistors in which the ratio of collector current to base current approaches infinity) are used will. If one assumes that the in Flg. 3 is in the operating mode as a voltage source, a reference voltage is determined by the Basls-Emltter voltages of transistors 30 and 33 plus the voltage drop across resistor 39. The dependent current source 46 drives equal collector currents into the transistors 30 and 31, so that a voltage AV _BE , which is dependent on the ratio of the EmUterbruche of the transistors 30 and 31, is impressed across the resistor 38. This voltage aV _Hf above resistance 38 also determines the operating collector currents of transistors 30-33 when the voltage feedback loop is complete. Mathematically, the voltage AV _aE and the corresponding collector currents of transistors 30 to 33 can be represented by equations 1 and 2 as follows:

(D Δν _ΒΕ = γΙ

(2) lao ^β / οι ^a Ιώϊ ^β fc » " η ^ '~ ξ

Where:

k = Boltzmann's constant

T = temperature in degrees Kelvin ⁿ

q = charge of the electron

- = 2.585 x 10- ² volts at 300 ° K

^q «Ι

- ⁱⁿ ^ e ₃₀ , A _E ) \ = emitter areas of transistors 30 and 31, respectively

R _n = resistance of resistor 38 In = natural logarithm

lao to Im = collector currents in transistors 30 to 33.

This voltage Δ V _BE , which can be used for calculation, has a positive temperature coefficient, as can be seen from the pachfoigenden equation:

If L ^{4 Vbe} 1 ⁼ -Sf ! J '"{ΑεΤοΙ J - 1 ^l " A _D0 T

dT LT "J 6T [q \ Abo IJQ ado ι ⁴ "

- [δ Kk] therefore has a positive temperature coefficient, because both Δ V _BE and Tposiiive are real numbers. Since npn transistors with a holiem beta value are assumed, the voltage across resistor 39 is:

39 Ol 39 ß _Jg q

and this must also have a positive temperature coefficient, since the ratio & ,: Rn is independent of temperature. Therefore, the voltage at the base of transistor 33 and between lines 42 un * 43, the reference voltage V ^ f, can be represented by the following equations (4) and (5):

(4) V ₁₁ Ef = V _BE30 + V _Bm + g · - In [^), or

V = 2V + - - In
H = Tnndctnnn in i.nri «aic i ^ onticrhp opfimptrischc structures are formed. Since the first link of the

since the transistors 30 and 33 are designed as identical geometric structures. Since the first term of equation (5) on the right-hand side has a negative temperature coefficient and the second term a positive temperature coefficient, it can be assumed that a set of values for R _x and R _{39 of} the reference voltage V _{REF have} a zero temperature coefficient confers. In the circuit under consideration, this occurs at V _REF = 2.56 volts. In a practically implemented integrated circuit, the value beta does not always have the very high value assumed above, so that the operation of the circuit is influenced to a small extent by the base currents of the various transistors. The effects of these finite beta values are kept very small by a resistor 40 which compensates for the base current errors.

PIe at terminal 36 output voltage is then according to the following equation (6) of the Bc / upsspnnnunp dependent:

₍₆₎ k «- ^^ V _Kf -

The output voltage at terminal 36 is essentially determined by the circuit within the dashed line 45, which has a zero temperature coefficient. V _RFF is generated between the lines 42 and 43 and controls the power supply 34. This is achieved because the current in the line 44, which is connected through terminal 44 'to the input of the current amplifier 35, changes as it does Is required to maintain the appropriate mathematical relationships of V _REf when the feedback loop through resistors 37 and 47 is closed. The combination of the current amplifier 35 and the power output transistor 34 operates as a power output stage. The output voltage V _m , at terminal 36 is kept at the desired value by the power output stage, regardless of the input voltage or the output load.

The operating mode of the error amplification of the circuit according to the invention can be seen from FIG. The functioning of this circuit as an amplifier is described below. If the voltage difference between the lines 42 and 43 is gradually increased from zero to a value which is higher than the reference voltage, the currents / _C3J and / _{c33 will increase} in the same way. Due to the relatively high resistance values of the resistors 38 and 39, which are of the order of magnitude of kilo-ohms , however, Iex increases essentially linearly with the voltage, while / _{C3] increases} approximately exponentially in that area. In the / _r]} «/ _ru « ^ £ lst. It is the act of closing the feedback squint around the

non-linear control amplifier through the In Flg. 3 shown resistors 37 and 47, which causes the compensation working currents of the transistors 30 to 33 to flow at the current value /) V _BE / R _n.

In the vicinity of the equilibrium operating current, the effects of any disturbances in the voltage on line 42 with respect to line 43 can be viewed as if they were observed at the amplifier output terminal 44. For these small disturbances, the change of the output current / can ', as a function of the small input ^2S voltage on line 42, namely, v "" be characterized as a linear function, and in the linear analysis of the small signal is a Stellheltsfunktlon (transconductance function) defined as g " = i, i, lv _aia . The transconductance of the circuit according to the present invention in the operation of the error converter can then be represented by equation (7):

\ ^gml ^ ⁺

[2 + g _m , (

\ ^gml '

ß ~ + J [2 + g _m , (A39 +

where a "is the steepness of the amplifier stage and is defined as the ratio of the change in the output current of the small signal to the change in the input voltage causing it, and according to the definition it is = / _a ," / v, i ".

It is

β = borrow transistor current gain

R _M and R ₃₉ are the resistance values of the resistors 38 and 39 in Fig. 4. In the preferred embodiment of the invention, the transconductance is about 250 microhms. Although the steepness of the amplifier stage is relatively low, an effectively working error amplifier can be represented if the load impedance at node 44 'is large. This requirement can easily be met with relatively simple circuit elements in the current amplifier 35, which only needs to enable a large current gain.

In operation, the range of direct current levels which are permissible for transistors 30 to 33 is between tenths of a microampere and approximately in the order of magnitude of milliamps. As a practical limit, the size of the surface of the chip must be taken into account, which the resistors A _M and R ₁₉ occupy if they are produced in monomial form. In any event, the range of current levels is wide enough and of an order of magnitude sufficient to allow the circuit to generate a reference voltage which is a practical fraction of the desired output voltage. The amplitude of the low alternating current signal which is generated at node 44 'by the error amplifier in accordance with Flg. 4 is generated is very low. To regulate 100 milliamps output DC current, the alternating current would be on the order of nanoamps or less. The alternating current assigned to the error amplifier is then significantly lower than the direct currents at the level of microamps which occur at the reference voltage source. Accordingly, the function of the reference voltage is not impaired by the fact that the function of the error amplifier is superimposed on it.

For this purpose 2 sheets of drawings

Claims (2)

Patent address: 1. Voltage regulator circuit with internal zero temperature coefficient reference voltage source, soft one Generates an output voltage that is proportional to a semiconductor material bandgap voltage, and with a Error amplifier and a voltage divider network connected to an output amplifier, wherein a . Input of the error amplifier with one branch of the voltage regulator network and another input with the reference voltage source and the output of the error amplifier is coupled to the input of the output amplifier, characterized in that the error amplifier and the reference voltage source are in the same integrated circuit, that the circuit has a first transistor (31) ίο has whose collector and base are electrically connected to the base of a second transistor (30), that the emitter of the second transistor (30) via a first resistor (38) with the emitter of the first Transistor (31) is electrically connected that the emitter of a third transistor (32) with the collector of the second transistor (30) is electrically connected that the emitter of a fourth transistor (33) with the Base of the third transistor (32) and via a second resistor (39) to the collector of the first is transistor (31) is electrically connected, and that the collectors of the third (32) and the fourth (33) Transistors are coupled to one another, the base of the fourth transistor (33) to the voltage controller (37, 47) and the collector of the third transistor (32) to the output of the error amplifier are connected. 2. Voltage regulator circuit according to spoke 1, characterized in that a third resistor (40) is switched on between the base of the second transistor (30) and the base of the first transistor (31).